1. Field of Invention
This invention relates to seat belt retractors and more particularly the seat belt retractors for retracting two seat belts.
2. Prior Art
Among seat belt systems which are used to insure the safety of passengers by securely restraining these passengers during vehicle emergencies such as collisions, etc., three point seat belt systems consisting of lap and shoulder restraining belts are widely employed. Among these three point seat beltsystems, the two belt retracting type of seat belt system has been offered as a system which employs only a single retractor mechanism without injuring the performance of the system.
As shown in FIG. 1, the two belt retracting type of seat belt system 1 consists of a retactor mechanism 2, a continuous restraining belt 3, a tongue plate 4 and a buckle 5. The continuous restraining belt 3 is formed in the shape of an endless loop.
One portion of the belt 3 is made to serve as the lap restraining belt 3A and the remaining portion is made to serve as the shoulder restraining belt 3B. The lap restraining belt 3A and the shoulder restraining belt 3B are taken up on a single take-up shaft of a retractor one over the other in the retracting mechnism 2. The portion of the belt 3 with the lap restraining belt 3A and the shoulder restraining belt 3B meet is passed freely through an opening 6 in a tongue plate 4. Furthermore, the intermediate portion of the shoulder restraining belt 3B is anchored by being freely passed through an eye in an anchor 7 which is fastened to the upper portion of the side wall of a vehicle body.
A seat belt system 1 thus constructed is designed so that the lap restraining belt 3A and the shoulder restraining belt 3B are caused to form a three point seat belt system by means of engaging the tongue plate 4 with the buckle 5 which is anchored near the center line of the vehicle body.
Furthermore, the lap restraining belt 3A and the shoulder restraining belt 3B can be passed freely through an opening 6 in the tongue plate 4. Accordingly, this system has offered improved performance in spite of the fact that only a single retractor mechanism 2 is employed.
The retractor mechanism 2 in this type of seat belt system 1 is equipped with a vehicle inertia sensitive type emergency engagement mechanism which quickly and securely stops the extension of the restraining belts during vehicle emergencies such as collisions, etc. This emergency extension stopping mechnism requires a sensitive sensing device which detects the abrupt deceleration of the vehicle or the abrupt extension of the continuous restraining belt and an engagement mechnism which responds to this sensor by locking the extension of the continuous restraining belt. Such a retractor mechanism has certain advantages but has certain other disadvantages. In particular, the sensitive sensor for the emergency extension stopping mechanism adds complexity to the retractor and detracts from its reliability. Furthermore, typically the sensor for the the vehicle inertia sensitive type emergency engagement mechanism requires that the seat belt retractor be mounted at some particular angle or some particular place in the vehicle.